Kinases are proteins involved in different cellular responses to external signals. In the Nineties, a new family of kinases called MAPK (mitogen-activated protein kinases) was discovered. MAPK activate their substrates by phosphorylation in serine and threonine residues.
MAPK are activated by other kinases in response to a wide range of signals including growth factors, pro-inflammatory cytokines, UV radiation, endotoxins and osmotic stress. Once they are activated, MAPK activate by phosphorylation other kinases or proteins, such as transcription factors, which, ultimately, induce an increase or a decrease in expression of a specific gene or group of genes.
The MAPK family includes kinases such as p38, ERK (extracellular-regulated protein kinase) and JNK (C-Jun N-terminal kinase).
Kinase p38 plays a crucial role in cellular response to stress and in the activation pathway in the synthesis of numerous cytokines, especially tumor necrosis factor (TNF-α), interleukin-1 (IL-1), interleukin-6 (IL-6) and interleukin-8 (IL-8).
IL-1 and TNF-α are produced by macrophages and monocytes and are involved in the mediation of immunoregulation processes and other physiopathological conditions. For example, elevated levels of TNF-α are associated with inflammatory and autoimmune diseases and with processes that trigger the degradation of connective and bone tissue such as rheumatoid arthritis, osteoarthritis, diabetes, inflammatory bowel disease and sepsis.
Thus, p38 kinase inhibitors could be useful to treat or prevent diseases mediated by cytokines such as IL-1 and TNF-α, as mentioned previously.
On the other hand, it has also been found that p38 inhibitors inhibit other pro-inflammatory proteins such as IL-6, IL-8, interferon-γ and GM-CSF (granulocyte-macrophage colony-stimulating factor). Moreover, in recent studies it has been found that p38 inhibitors not only block cytokine synthesis but also the cascade of signals that these induce, such as induction of the cyclooxygenase-2 enzyme (COX-2).